1. Field of the Invention
This invention concerns devices for checking machined workpieces, and more particularly devices for checking surfaces of workpieces to verify the presence of threads and also to detect various abnormal test piece conditions.
2. Description of the Prior Art
In U.S. Pat. No. 4,437,335, there is disclosed a device for accomplishing the above objective, in which a probe spindle is pivotally mounted in a housing, the probe having an attached elongated probe tip extending from one end thereof. The proble spindle is slidably movable to the rear within a probe body, and has an internal passage supplied with air under pressure exiting through a side outlet adjacent the tip end.
The probe device is moved towards the presumed location of the bore in the workpiece in the first phase of the test, and if the probe tip encounters either a broken tool or an unformed bore, the air flow is throttled by movement of the tip back into the probe body, which condition in turn is detected as a back pressure increase by a pressure switch mounted in the probe housing.
In a second phase, initiated after the probe tip has moved within the test piece bore, the probe spindle is tilted about a pivot axis by a side mounted piston. If the probe moves too far before encountering the side wall of the test piece bore, a limit switch is tripped, providing a fault condition signal for an oversize bore, or the absence of the probe tip or the test piece itself.
When the probe tip does encounter the bore sidewall, that surface will substantially block outflow from the probe tip, unless threads are present, to again cause increased back pressure, which blockage is detected by the pressure switch to generate a "no thread" fault condition signal.
In copending application Ser. No. 845,956, filed on Mar. 31, 1986, assigned to the same assignee as the present application, there is disclosed an improved version of this device, in which refinements are made of the actuation of the pivoting of the probe, and for the arrangement for mounting of the unit to a tooling plate.
The pivoting motion of the probe has disadvantages, particularly for an increased extent of pivoting travel, in that tilting of the probe spindle allows the tip air outlet to become skewed with respect to the test surface, allowing escape of air despite being positioned against the surface. Any tendency for this to occur obviously reduces the reliability of obtaining an increased back pressure reading when the surface is unthreaded. That is, if air leakage occurs due to tilting of the tip, this could mask the absence of threads on the tested surface in that an increased back pressure would not occur despite the absence of threads.
The pivoting of the probe also limits the range of motion able to be achieved by a reasonably compact device. The range of tip motion available to move the tip against the bore sidewall is important as this allows lower tolerances in the position error of the probe tip within the bore to be tested. In addition, the range of travel improves the reliability of the over limit movement detection phase of the test.